On the use of the Combined Loading Compression fixture to estimate the intralaminar compressive fracture toughness of composites

• Published in: Engineering fracture mechanics 2023-09, Vol.289, p.109444, Article 109444
• Main Authors: Dalli, D., Danzi, F., Silva Campos, P.J., Arteiro, A., Camanho, P.P.
• Format: Article
• Language: English
• Subjects: Analytical modelling; Composites; Compressive intralaminar fracture toughness; Mechanical testing; Size-effect method
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2023.109444

•Assessment of CLC fixture constraint on notched composite specimens.•Experimental characterisation using UD thermoplastic and 2D woven thermoset composites.•Original constraint assumption resulted in significant underestimation of compressive fracture toughness.•DENC specimen testing also shown to provide an underestimation of this value.•New interpretation of CLC constraint effects results in higher fracture toughness estimates. This study reassesses the constraint effect provided by a Combined Loading Compression (CLC) fixture on notched specimens used to measure the compressive intralaminar fracture toughness of composite materials. An experimental campaign is carried out to determine whether a variation in the specimen gauge section length would result in a significant change in the nominal strength of Double Edge Notch CLC specimens. Following the testing of six sets of different specimen geometries for both a uni-directional thermoplastic and a bi-directional woven thermoset composite, the effect of the gauge length is analysed using the size-effect method. Results show that nominal notched strength variation is minimal, suggesting that the CLC clamp does not effectively constrain the gripped sections against in-plane deformations. This assessment proves that the correction factor used in the determination of the R-curve needs to be computed considering the entire specimen geometry, including the gripped regions. Furthermore, the results reveal that previous characterisation campaigns conducted using end-loaded Double Edge Notch Compression specimens could have led to a significant underestimation of the steady-state fracture toughness.